1. Field of the Invention
The present invention relates to design of an integrated circuit device, and more particularly to a method and an apparatus for designing an integrated circuit device which comprises a transistor having a gate oxide film connected to conductive members.
2. Description of the Related Art
Presently, various integrated circuit devices are utilized in various electronic equipment. Such integrated circuit devices typically have various circuit components formed with a thin film technique. Such circuit components formed in an integrated circuit device with a thin film technique include a transistor whose gate oxide film may be connected to conductive members.
For example, in integrated circuit device 1 in the process of fabrication illustrated in FIG. 1, transistor 2 has gate oxide film 3 connected to gate electrode 4 and metal wire 5 as conductive members, and metal wire 5 is disposed on an upper surface of insulating layer 6 which is an insulating member. Photoresist 7 which is an insulating member is temporarily stacked as a mask on an surface of metal wire 5. Metal wire 5 is processed with anisotropic etching using plasma with photoresist 7 as a mask.
In integrated circuit device 1 in the aforementioned state, side surfaces of metal wire 5 are exposed to plasma and may be subjected to charge in the plasma at the anisotropic etching of metal wire 5. Since the charge entered by metal wire 5 flows from gate electrode 4 to semiconductor substrate 8 through gate oxide film 3, gate oxide film 3 may be damaged.
The presence or absence of the damage results from the density of the charge flowing through gate oxide film 3, and the charge density results from the intensity of the plasma, the area of gate oxide film 3 and the antenna size of metal wire 5. In other words, if the intensity of plasma used in the fabrication process is known, design may be performed only in consideration of the area of gate oxide film 3 and the antenna size of metal wire 5.
Thus, conventionally, a maximum antenna size M1 of conductive members allowed with respect to a reference area S1 of a gate oxide film is defined, and the ratio of the two is represented as an antenna ratio R, as follows:
R=M1/S1
When a gate oxide film with an area S2 is newly formed, an antenna size M2 of conductive members connected thereto can prevent damage to the gate oxide film if it is set as follows:
xe2x80x83M2xe2x89xa6Rxc3x97S2
It should be noted that the antenna size of conductive members refers to the size of portions of the conductive members which serve as an antenna, for example the area of exposed portions of the metal wire as described above. However, when a reference metal wire and a new metal wire have the same film thickness, the antenna size can be approximated by the area of an upper surface of the metal wire if only the upper surface of the metal wire is exposed, while the antenna size can be approximated by the entire periphery of the metal wire if only side surfaces thereof are exposed.
When a structure having conductive members connected to a gate oxide film is formed, any charge in plasma entered by the conductive members does not damage the gate oxide film if the relationship of an area S of the gate oxide film and an antenna size M of the conductive members to an antenna ratio R satisfies the following expression:
Mxe2x89xa6Rxc3x97S
However, when a maximum antenna size M1 of conductive members allowed with respect to a reference area S1 of a gate oxide film is specified, the specified ratio used as an antenna ratio R for calculating a maximum antenna size M2 with respect to a new area S2 revealed that the resulting antenna size M2 is inappropriate.
For example, assuming that a new area S2 being a double reference area S1, a new maximum antenna size M2 is also a double reference maximum antenna size M1 in the conventional approach. Actually, however, experiments show that the antenna size M2 more than doubles the antenna size M1 is allowed.
Additionally, assuming that a new area S2 is a half of a reference area S1, a new maximum antenna size M2 is also a half of a reference maximum antenna size M1 in the conventional approach. Actually, however, it has been shown that the antenna size M2 needs to be smaller than a half of the antenna size M1.
Specifically, changes in antenna size M of conductive members have been conventionally considered to be directly proportional to changes in area S of a gate oxide film at a certain antenna ratio R, which proved not to fit the actual conditions. As a result, the conventional approach can not form conductive members in a proper shape, thereby making it difficult to optimize integrated circuit devices.
It is an object of the present invention to provide a circuit design method and apparatus for optimally designing an integrated circuit device.
It is another object of the present invention to provide an information storage medium for storing a program for optimally designing an integrated circuit device.
It is further object of the present invention to provide an integrated circuit device in which conductive members connected to a gate oxide film of a transistor are formed in a proper shape.
A conventional circuit design method to which the present invention is applied is for designing an integrated circuit device having a transistor with a gate oxide film connected to conductive members wherein a maximum antenna size M1 of the conductive members allowed with respect to a reference area S1 of the gate oxide film is defined.
In a first aspect of the circuit design method of the present invention, when a gate oxide film having an area S2 larger than the area S1 is newly designed, a maximum antenna size M2 of new conductive members allowed with respect to the area S2 is set as follows:
M2 greater than M1xc3x97(S2/S1).
When a gate oxide film having an area S2 smaller than the area S1 is newly designed, a maximum antenna size M2 of new conductive members allowed with respect to the area S2 is set as follows:
M2 less than M1xc3x97(S2/S1).
In a second aspect of the circuit design method of the present invention, an area S2 of a new gate oxide film and a maximum antenna size M2 of new conductive members are set to satisfy the following relationship:
M2=M1xc3x97(S2/S1)1/b
where b is a predetermined constant.
In a third aspect of the circuit design method of the present invention, an area S2 of a new gate oxide film and a maximum antenna size M2 of new conductive members are set to satisfy the following relationship:
M2=dxc3x97(M1/d)(S2/S1)
where d is a predetermined constant.
In the aforementioned circuit design method, the constant b may satisfy 0.5xe2x89xa6bxe2x89xa60.8.
In the aforementioned circuit design method, the constant d may satisfy 0.5xe2x89xa6dxe2x89xa63.0.
In a first aspect of a circuit design apparatus of the present invention, data storage means stores an allowed maximum antenna size M1 of conductive members and a reference area S1 of a gate oxide film, and upon data input of an area S2 of a new gate oxide film to data input means, calculation means calculates a maximum antenna size M2 of new conductive members allowed with respect to the input area S2 as follows:
M2=M1xc3x97(S2/S1)1/b
where b is a predetermined constant.
In a second aspect of the circuit design apparatus of the present invention, data storage means stores an allowed maximum antenna size M1 of conductive members and a reference area S1 of a gate oxide film, and upon data input of an area S2 of a new gate oxide film to data input means, calculation means calculates a maximum antenna size M2 of new conductive members allowed with respect to the input area S2 as follows:
M2=dxc3x97(M1/d)(S2/S1)
where d is a predetermined constant.
An information storage medium of the present invention stores programs for causing a computer to perform processing in the circuit design method of the present invention. An integrated circuit device of the present invention is designed with the circuit design method of the present invention.
As described above, experiments show that changes in antenna size M of conductive members are not proportional to changes in area S of a gate oxide film. A relationship between antenna sizes M and charge amounts Q flowing into a gate oxide film, which are obtained as the experiment results, is plotted as FIG. 5.
Since the degree of damage to a gate oxide film is defined with the proportion of the area S to the charge amount Q, mathematization of curves in FIG. 5 obtained from the experiment results means mathematization of a relationship between the area S of a gate oxide film and the antenna size M of conductive members. Thus, consideration was given to expressions representing curves which approximate the experiment results and revealed that curves represented by the following two expressions approximate the experiment results:
Q=aMb (a, b are predetermined constants)xe2x80x83xe2x80x83(1)
Q=c log(M/d) (c, d are predetermined constants)xe2x80x83xe2x80x83(2)
When a maximum antenna size M1 of conductive members allowed with respect to a reference area S1 of a gate oxide film is defined, a charge amount Q2 allowed by a gate oxide film with an area S2 satisfies the following relationship assuming that a charge amount allowed by a gate oxide film with an area S1 is Q1:
Q1/S1=Q2/S2xe2x80x83xe2x80x83(3)
Substitution of the expression (1) into the expression (3) yields the following:
aM1b/S1=aM2b/S2xe2x80x83xe2x80x83(4)
and when the expression is simplified, the following is obtained:
M2=M1xc3x97(S2/S1)1/bxe2x80x83xe2x80x83(5)
Substitution of the expression (2) into the expression (3) yields the following:
c log(M1/d)/S1=c log(M2/d)/S2xe2x80x83xe2x80x83(6)
and when the expression is simplified, the following is obtained:
M2=dxc3x97(M1/d)(S2/S1).
Specifically, when a maximum antenna size M1 of conductive members allowed with respect to a reference area S1 of a gate oxide film is defined, an antenna size of conductive members is proper if an area S2 of a new gate oxide film and a maximum antenna size M2 of new conductive members satisfy the following relationship:
M2=M1xc3x97(S2/S1)1/b
where b is a predetermined constant, or the following relationship:
M2=dxc3x97(M1/d)(S2/S1)
where d is a predetermined constant.
In other words, in the present invention, an antenna size of conductive members is calculated with respect to a gate oxide film of a transistor using expressions which approximate an actual relationship of changes therein. As a result, it is possible to properly acquire an antenna size of conductive members connectable to a gate oxide film of a transistor, thereby enabling optimal design and fabrication of an integrated circuit device. Additionally, since design of an integrated circuit device need not be changed unnecessarily, an integrated circuit of optimal structure can be designed with favorable efficiency.
It should be noted that the constants b and d reflect the proportion of damage to the antenna size of conductive members. The constant b preferably satisfies, for example, xe2x80x9c0.5xe2x89xa6bxe2x89xa60.8xe2x80x9d, and can be set to approximately 0.64.
The constant d preferably satisfies xe2x80x9c0.5xe2x89xa6dxe2x89xa63.0xe2x80x9d, and can be set to approximately 1.39.
Various means in the present invention may be formed in any way to realize their functions, and for example, dedicated hardware, computers provided with proper functions by programs, functions realized within computers by proper programs, or a combination thereof is allowed.
The antenna size of conductive members in the present invention refers to the size of portions of the conductive members which serve as an antenna, for example the area of exposed portions of a metal wire. However, when a reference metal wire and a new metal wire have the same film thickness, the antenna size can be approximated by the area of an upper surface of the metal wire if only the upper surface of the metal wire is exposed, while the antenna size can be approximated by the entire periphery of the metal wire if only side surfaces thereof are exposed.
The information storage medium in the present invention may be any medium which previously stores programs as software for causing computers to perform various processing, and for example, ROMs (Read Only Memory) or HDDs (Hard Disc Drive) fixed in a device having a computer as a portion thereof, CD (Compact Disk)-ROMs or FDs (Floppy Disk) loaded removably on a device having a computer as a portion thereof, or the like is allowed.
The computer in the present invention may be any device as long as it can read programs comprising software to perform processing which corresponds thereto, and for example, an apparatus having a CPU (Central Processing Unit) as a main unit and various devices such as ROM, RAM, I/F (interface) or the like connected thereto as required is allowed.
The above and other object, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.